1. Field of the Invention
The present invention relates generally to the fields of optics, lasers and medical diagnostics. More specifically, the present invention relates to a novel method of measuring tissue optical properties using a optical beam of oblique incidence and uses thereof.
2. Description of the Related Art
In both diagnostic and therapeutic applications of light in medicine, it is important to evaluate optical properties of tissues, including the absorption coefficient (.mu..sub.a) and the reduced scattering coefficient [.mu..sub.s '=.mu..sub.s (1-g)], where .mu..sub.s is the scattering coefficient and g is the anisotropy factor of scattering. The optical properties can be used to diagnose diseases, to measure tissue metabolic status, or to determine the dosimetry in therapeutic applications of lasers. Measuring optical properties of tissues in vitro can be accomplished by several techniques, with the integrating sphere measurement as the most common (Pickering, J. W. et al., Appl. Opt.; 32:399-410 (1993)). Measuring optical properties of tissues in vivo is still a challenge.
Wilson et al. (Wilson, B. C. et al., Proc. Soc. Photo-Opt. Instrum. Eng.; IS6:219-232 (1990)) have used an optical fiber bundle and Jacques et al. (Jacques S. L. et al., Proc. Soc. Photo-Opt. Instrum. Eng.; IS11:211-226 (1993)) a video reflectometer to measure diffuse reflectance of tissues in vivo. Diffusion theory has been used to compute diffuse reflectance to deduce optical properties. Diffusion theory is valid for an infinitely narrow laser beam and for observation points far from the light source, but a laser beam of a finite size is used for measurement of diffuse reflectance. Therefore, diffusion theory is only approximately correct. Another method represented by Patterson et al. uses the falling tail of time-resolved diffuse reflectance to deduce tissue optical properties but requires expensive instrumentation.
The prior art is deficient in the lack of an accurate method of measuring tissue optical properties. The present invention fulfills this longstanding need and desire in the art.